diff --git a/docs/BACKEND_REFACTOR_PLAN.md b/docs/BACKEND_REFACTOR_PLAN.md
index 48bb582..a11546f 100644
--- a/docs/BACKEND_REFACTOR_PLAN.md
+++ b/docs/BACKEND_REFACTOR_PLAN.md
@@ -79,6 +79,9 @@
 - **阶段 3：补充测试 🚧**  
   - `tests/import_export_sync.rs` 集成测试涵盖配置备份、Claude/Codex live 同步、MCP 投影与 Codex/Claude 双向导入流程，并新增启用项清理、非法 TOML 抛错等失败场景验证；统一使用隔离 HOME 目录避免污染真实用户环境。  
   - 扩展 `lib.rs` re-export，暴露 `AppType`、`MultiAppConfig`、`AppError`、配置 IO 以及 Codex/Claude MCP 路径与同步函数，方便服务层及测试直接复用核心逻辑。  
+  - 新增负向测试验证 Codex 供应商缺少 `auth` 字段时的错误返回，并补充备份数量上限测试；顺带修复 `create_backup` 采用内存读写避免拷贝继承旧的修改时间，确保最新备份不会在清理阶段被误删。  
+  - 针对 `codex_config::write_codex_live_atomic` 补充成功与失败场景测试，覆盖 auth/config 原子写入与失败回滚逻辑（模拟目标路径为目录时的 rename 失败），降低 Codex live 写入回归风险。  
+  - 新增 `tests/provider_commands.rs` 覆盖 `switch_provider` 的 Codex 正常流程与供应商缺失分支，并抽取 `switch_provider_internal` 以复用 `AppError`，通过 `switch_provider_test_hook` 暴露测试入口；同时共享 `tests/support.rs` 提供隔离 HOME / 互斥工具函数。  
   - 当前已覆盖配置、Codex/Claude MCP 核心路径及关键错误分支，后续仍需补齐命令层边界与导入导出异常回滚测试。
 
 ## 渐进式重构路线
diff --git a/src-tauri/src/commands/provider.rs b/src-tauri/src/commands/provider.rs
index 2e7f779..cbaa46a 100644
--- a/src-tauri/src/commands/provider.rs
+++ b/src-tauri/src/commands/provider.rs
@@ -8,6 +8,7 @@ use tauri::State;
 use crate::app_config::AppType;
 use crate::codex_config;
 use crate::config::get_claude_settings_path;
+use crate::error::AppError;
 use crate::provider::{Provider, ProviderMeta};
 use crate::speedtest;
 use crate::store::AppState;
@@ -310,44 +311,32 @@ pub async fn delete_provider(
 }
 
 /// 切换供应商
-#[tauri::command]
-pub async fn switch_provider(
-    state: State<'_, AppState>,
-    app_type: Option<AppType>,
-    app: Option<String>,
-    appType: Option<String>,
-    id: String,
-) -> Result<bool, String> {
-    let app_type = app_type
-        .or_else(|| app.as_deref().map(|s| s.into()))
-        .or_else(|| appType.as_deref().map(|s| s.into()))
-        .unwrap_or(AppType::Claude);
+fn switch_provider_internal(state: &AppState, app_type: AppType, id: &str) -> Result<(), AppError> {
+    use serde_json::Value;
 
     let mut config = state
         .config
         .lock()
-        .map_err(|e| format!("获取锁失败: {}", e))?;
+        .map_err(|e| AppError::Message(format!("获取锁失败: {}", e)))?;
 
     let provider = {
         let manager = config
             .get_manager_mut(&app_type)
-            .ok_or_else(|| format!("应用类型不存在: {:?}", app_type))?;
+            .ok_or_else(|| AppError::Message(format!("应用类型不存在: {:?}", app_type)))?;
 
         manager
             .providers
-            .get(&id)
-            .ok_or_else(|| format!("供应商不存在: {}", id))?
-            .clone()
+            .get(id)
+            .cloned()
+            .ok_or_else(|| AppError::Message(format!("供应商不存在: {}", id)))?
     };
 
     match app_type {
         AppType::Codex => {
-            use serde_json::Value;
-
             if !{
                 let cur = config
                     .get_manager_mut(&app_type)
-                    .ok_or_else(|| format!("应用类型不存在: {:?}", app_type))?;
+                    .ok_or_else(|| AppError::Message(format!("应用类型不存在: {:?}", app_type)))?;
                 cur.current.is_empty()
             } {
                 let auth_path = codex_config::get_codex_auth_path();
@@ -356,7 +345,11 @@ pub async fn switch_provider(
                     let auth: Value = crate::config::read_json_file(&auth_path)?;
                     let config_str = if config_path.exists() {
                         std::fs::read_to_string(&config_path).map_err(|e| {
-                            format!("读取 config.toml 失败: {}: {}", config_path.display(), e)
+                            AppError::Message(format!(
+                                "读取 config.toml 失败: {}: {}",
+                                config_path.display(),
+                                e
+                            ))
                         })?
                     } else {
                         String::new()
@@ -370,12 +363,12 @@ pub async fn switch_provider(
                     let cur_id2 = {
                         let m = config
                             .get_manager(&app_type)
-                            .ok_or_else(|| format!("应用类型不存在: {:?}", app_type))?;
+                            .ok_or_else(|| AppError::Message(format!("应用类型不存在: {:?}", app_type)))?;
                         m.current.clone()
                     };
                     let m = config
                         .get_manager_mut(&app_type)
-                        .ok_or_else(|| format!("应用类型不存在: {:?}", app_type))?;
+                        .ok_or_else(|| AppError::Message(format!("应用类型不存在: {:?}", app_type)))?;
                     if let Some(cur) = m.providers.get_mut(&cur_id2) {
                         cur.settings_config = live;
                     }
@@ -385,7 +378,7 @@ pub async fn switch_provider(
             let auth = provider
                 .settings_config
                 .get("auth")
-                .ok_or_else(|| "目标供应商缺少 auth 配置".to_string())?;
+                .ok_or_else(|| AppError::Message("目标供应商缺少 auth 配置".to_string()))?;
             let cfg_text = provider
                 .settings_config
                 .get("config")
@@ -401,14 +394,14 @@ pub async fn switch_provider(
                 let cur_id = {
                     let m = config
                         .get_manager(&app_type)
-                        .ok_or_else(|| format!("应用类型不存在: {:?}", app_type))?;
+                        .ok_or_else(|| AppError::Message(format!("应用类型不存在: {:?}", app_type)))?;
                     m.current.clone()
                 };
                 if !cur_id.is_empty() {
                     if let Ok(live) = read_json_file::<serde_json::Value>(&settings_path) {
                         let m = config
                             .get_manager_mut(&app_type)
-                            .ok_or_else(|| format!("应用类型不存在: {:?}", app_type))?;
+                            .ok_or_else(|| AppError::Message(format!("应用类型不存在: {:?}", app_type)))?;
                         if let Some(cur) = m.providers.get_mut(&cur_id) {
                             cur.settings_config = live;
                         }
@@ -417,7 +410,8 @@ pub async fn switch_provider(
             }
 
             if let Some(parent) = settings_path.parent() {
-                std::fs::create_dir_all(parent).map_err(|e| format!("创建目录失败: {}", e))?;
+                std::fs::create_dir_all(parent)
+                    .map_err(|e| AppError::Message(format!("创建目录失败: {}", e)))?;
             }
 
             write_json_file(&settings_path, &provider.settings_config)?;
@@ -426,8 +420,8 @@ pub async fn switch_provider(
                 if let Ok(live_after) = read_json_file::<serde_json::Value>(&settings_path) {
                     let m = config
                         .get_manager_mut(&app_type)
-                        .ok_or_else(|| format!("应用类型不存在: {:?}", app_type))?;
-                    if let Some(target) = m.providers.get_mut(&id) {
+                        .ok_or_else(|| AppError::Message(format!("应用类型不存在: {:?}", app_type)))?;
+                    if let Some(target) = m.providers.get_mut(id) {
                         target.settings_config = live_after;
                     }
                 }
@@ -438,8 +432,8 @@ pub async fn switch_provider(
     {
         let manager = config
             .get_manager_mut(&app_type)
-            .ok_or_else(|| format!("应用类型不存在: {:?}", app_type))?;
-        manager.current = id;
+            .ok_or_else(|| AppError::Message(format!("应用类型不存在: {:?}", app_type)))?;
+        manager.current = id.to_string();
     }
 
     if let AppType::Codex = app_type {
@@ -450,12 +444,12 @@ pub async fn switch_provider(
         let cur_id = {
             let m = config
                 .get_manager(&app_type)
-                .ok_or_else(|| format!("应用类型不存在: {:?}", app_type))?;
+                .ok_or_else(|| AppError::Message(format!("应用类型不存在: {:?}", app_type)))?;
             m.current.clone()
         };
         let m = config
             .get_manager_mut(&app_type)
-            .ok_or_else(|| format!("应用类型不存在: {:?}", app_type))?;
+            .ok_or_else(|| AppError::Message(format!("应用类型不存在: {:?}", app_type)))?;
         if let Some(p) = m.providers.get_mut(&cur_id) {
             if let Some(obj) = p.settings_config.as_object_mut() {
                 obj.insert(
@@ -471,7 +465,34 @@ pub async fn switch_provider(
     drop(config);
     state.save()?;
 
-    Ok(true)
+    Ok(())
+}
+
+#[doc(hidden)]
+pub fn switch_provider_test_hook(
+    state: &AppState,
+    app_type: AppType,
+    id: &str,
+) -> Result<(), AppError> {
+    switch_provider_internal(state, app_type, id)
+}
+
+#[tauri::command]
+pub async fn switch_provider(
+    state: State<'_, AppState>,
+    app_type: Option<AppType>,
+    app: Option<String>,
+    appType: Option<String>,
+    id: String,
+) -> Result<bool, String> {
+    let app_type = app_type
+        .or_else(|| app.as_deref().map(|s| s.into()))
+        .or_else(|| appType.as_deref().map(|s| s.into()))
+        .unwrap_or(AppType::Claude);
+
+    switch_provider_internal(&state, app_type, &id)
+        .map(|_| true)
+        .map_err(|e| e.to_string())
 }
 
 /// 导入当前配置为默认供应商
diff --git a/src-tauri/src/import_export.rs b/src-tauri/src/import_export.rs
index f0b58f2..8a6d43e 100644
--- a/src-tauri/src/import_export.rs
+++ b/src-tauri/src/import_export.rs
@@ -28,8 +28,8 @@ pub fn create_backup(config_path: &PathBuf) -> Result<String, AppError> {
 
     let backup_path = backup_dir.join(format!("{}.json", backup_id));
 
-    // 复制配置文件到备份
-    fs::copy(config_path, &backup_path).map_err(|e| AppError::io(&backup_path, e))?;
+    let contents = fs::read(config_path).map_err(|e| AppError::io(config_path, e))?;
+    fs::write(&backup_path, contents).map_err(|e| AppError::io(&backup_path, e))?;
 
     // 备份完成后清理旧的备份文件（仅保留最近 MAX_BACKUPS 份）
     cleanup_old_backups(&backup_dir, MAX_BACKUPS)?;
diff --git a/src-tauri/src/lib.rs b/src-tauri/src/lib.rs
index d1b48bd..84e0b5a 100644
--- a/src-tauri/src/lib.rs
+++ b/src-tauri/src/lib.rs
@@ -16,15 +16,16 @@ mod store;
 mod usage_script;
 
 pub use app_config::{AppType, MultiAppConfig};
-pub use codex_config::{get_codex_auth_path, get_codex_config_path};
+pub use codex_config::{get_codex_auth_path, get_codex_config_path, write_codex_live_atomic};
 pub use config::{get_claude_mcp_path, get_claude_settings_path, read_json_file};
 pub use import_export::{create_backup, sync_current_providers_to_live};
 pub use provider::Provider;
 pub use settings::{update_settings, AppSettings};
 pub use mcp::{import_from_claude, import_from_codex, sync_enabled_to_claude, sync_enabled_to_codex};
 pub use error::AppError;
+pub use store::AppState;
+pub use commands::*;
 
-use store::AppState;
 use tauri::{
     menu::{CheckMenuItem, Menu, MenuBuilder, MenuItem},
     tray::{TrayIconBuilder, TrayIconEvent},
diff --git a/src-tauri/tests/import_export_sync.rs b/src-tauri/tests/import_export_sync.rs
index 281fc32..2b74ca5 100644
--- a/src-tauri/tests/import_export_sync.rs
+++ b/src-tauri/tests/import_export_sync.rs
@@ -1,52 +1,14 @@
 use std::fs;
-use std::path::Path;
 use serde_json::json;
-use std::sync::{Mutex, OnceLock};
 
 use cc_switch_lib::{
-    create_backup, get_claude_settings_path, read_json_file, sync_current_providers_to_live,
-    update_settings, AppSettings, AppType, MultiAppConfig, Provider,
+    create_backup, get_claude_settings_path, read_json_file, sync_current_providers_to_live, AppType,
+    MultiAppConfig, Provider,
 };
 
-fn ensure_test_home() -> &'static Path {
-    static HOME: OnceLock<std::path::PathBuf> = OnceLock::new();
-    HOME.get_or_init(|| {
-        let base = std::env::temp_dir().join("cc-switch-test-home");
-        if base.exists() {
-            let _ = std::fs::remove_dir_all(&base);
-        }
-        std::fs::create_dir_all(&base).expect("create test home");
-        std::env::set_var("HOME", &base);
-        #[cfg(windows)]
-        std::env::set_var("USERPROFILE", &base);
-        base
-    })
-    .as_path()
-}
-
-fn reset_test_fs() {
-    let home = ensure_test_home();
-    for sub in [".claude", ".codex", ".cc-switch"] {
-        let path = home.join(sub);
-        if path.exists() {
-            if let Err(err) = fs::remove_dir_all(&path) {
-                eprintln!("failed to clean {}: {}", path.display(), err);
-            }
-        }
-    }
-    let claude_json = home.join(".claude.json");
-    if claude_json.exists() {
-        let _ = fs::remove_file(&claude_json);
-    }
-    // 重置内存中的设置缓存，确保测试环境不受上一次调用影响
-    // 写入默认设置即可刷新 OnceLock 中的缓存数据
-    let _ = update_settings(AppSettings::default());
-}
-
-fn test_mutex() -> &'static Mutex<()> {
-    static MUTEX: OnceLock<Mutex<()>> = OnceLock::new();
-    MUTEX.get_or_init(|| Mutex::new(()))
-}
+#[path = "support.rs"]
+mod support;
+use support::{ensure_test_home, reset_test_fs, test_mutex};
 
 #[test]
 fn sync_claude_provider_writes_live_settings() {
@@ -287,6 +249,129 @@ fn sync_enabled_to_codex_returns_error_on_invalid_toml() {
     }
 }
 
+#[test]
+fn sync_codex_provider_missing_auth_returns_error() {
+    let _guard = test_mutex().lock().expect("acquire test mutex");
+    reset_test_fs();
+
+    let mut config = MultiAppConfig::default();
+    let provider = Provider::with_id(
+        "codex-missing-auth".to_string(),
+        "No Auth".to_string(),
+        json!({
+            "config": "model = \"test\""
+        }),
+        None,
+    );
+    let manager = config
+        .get_manager_mut(&AppType::Codex)
+        .expect("codex manager");
+    manager.providers.insert(provider.id.clone(), provider);
+    manager.current = "codex-missing-auth".to_string();
+
+    let err = sync_current_providers_to_live(&mut config)
+        .expect_err("sync should fail when auth missing");
+    match err {
+        cc_switch_lib::AppError::Config(msg) => {
+            assert!(msg.contains("auth"), "error message should mention auth");
+        }
+        other => panic!("unexpected error variant: {other:?}"),
+    }
+
+    // 确认未产生任何 live 配置文件
+    assert!(
+        !cc_switch_lib::get_codex_auth_path().exists(),
+        "auth.json should not be created on failure"
+    );
+    assert!(
+        !cc_switch_lib::get_codex_config_path().exists(),
+        "config.toml should not be created on failure"
+    );
+}
+
+#[test]
+fn write_codex_live_atomic_persists_auth_and_config() {
+    let _guard = test_mutex().lock().expect("acquire test mutex");
+    reset_test_fs();
+
+    let auth = json!({ "OPENAI_API_KEY": "dev-key" });
+    let config_text = r#"
+[mcp_servers.echo]
+type = "stdio"
+command = "echo"
+args = ["ok"]
+"#;
+
+    cc_switch_lib::write_codex_live_atomic(&auth, Some(config_text))
+        .expect("atomic write should succeed");
+
+    let auth_path = cc_switch_lib::get_codex_auth_path();
+    let config_path = cc_switch_lib::get_codex_config_path();
+    assert!(auth_path.exists(), "auth.json should be created");
+    assert!(config_path.exists(), "config.toml should be created");
+
+    let stored_auth: serde_json::Value =
+        cc_switch_lib::read_json_file(&auth_path).expect("read auth");
+    assert_eq!(stored_auth, auth, "auth.json should match input");
+
+    let stored_config = std::fs::read_to_string(&config_path).expect("read config");
+    assert!(
+        stored_config.contains("mcp_servers.echo"),
+        "config.toml should contain serialized table"
+    );
+}
+
+#[test]
+fn write_codex_live_atomic_rolls_back_auth_when_config_write_fails() {
+    let _guard = test_mutex().lock().expect("acquire test mutex");
+    reset_test_fs();
+
+    let auth_path = cc_switch_lib::get_codex_auth_path();
+    if let Some(parent) = auth_path.parent() {
+        std::fs::create_dir_all(parent).expect("create codex dir");
+    }
+    std::fs::write(&auth_path, r#"{"OPENAI_API_KEY":"legacy"}"#).expect("seed auth");
+
+    let config_path = cc_switch_lib::get_codex_config_path();
+    std::fs::create_dir_all(&config_path).expect("create blocking directory");
+
+    let auth = json!({ "OPENAI_API_KEY": "new-key" });
+    let config_text = r#"[mcp_servers.sample]
+type = "stdio"
+command = "noop"
+"#;
+
+    let err = cc_switch_lib::write_codex_live_atomic(&auth, Some(config_text))
+        .expect_err("config write should fail when target is directory");
+    match err {
+        cc_switch_lib::AppError::Io { path, .. } => {
+            assert!(
+                path.ends_with("config.toml"),
+                "io error path should point to config.toml"
+            );
+        }
+        cc_switch_lib::AppError::IoContext { context, .. } => {
+            assert!(
+                context.contains("config.toml"),
+                "error context should mention config path"
+            );
+        }
+        other => panic!("unexpected error variant: {other:?}"),
+    }
+
+    let stored = std::fs::read_to_string(&auth_path).expect("read existing auth");
+    assert!(
+        stored.contains("legacy"),
+        "auth.json should roll back to legacy content"
+    );
+    assert!(
+        std::fs::metadata(&config_path)
+            .expect("config path metadata")
+            .is_dir(),
+        "config path should remain a directory after failure"
+    );
+}
+
 #[test]
 fn import_from_codex_adds_servers_from_mcp_servers_table() {
     let _guard = test_mutex().lock().expect("acquire test mutex");
@@ -533,3 +618,56 @@ fn create_backup_generates_snapshot_file() {
         "backup content should match original config"
     );
 }
+
+#[test]
+fn create_backup_retains_only_latest_entries() {
+    let _guard = test_mutex().lock().expect("acquire test mutex");
+    reset_test_fs();
+    let home = ensure_test_home();
+    let config_dir = home.join(".cc-switch");
+    let config_path = config_dir.join("config.json");
+    fs::create_dir_all(&config_dir).expect("prepare config dir");
+    fs::write(&config_path, r#"{"version":3}"#).expect("write config file");
+
+    let backups_dir = config_dir.join("backups");
+    fs::create_dir_all(&backups_dir).expect("create backups dir");
+    for idx in 0..12 {
+        let manual = backups_dir.join(format!("manual_{idx:02}.json"));
+        fs::write(&manual, format!("{{\"idx\":{idx}}}")).expect("seed manual backup");
+    }
+
+    std::thread::sleep(std::time::Duration::from_secs(1));
+
+    let latest_backup_id = create_backup(&config_path).expect("create backup with cleanup");
+    assert!(
+        !latest_backup_id.is_empty(),
+        "backup id should not be empty when config exists"
+    );
+
+    let entries: Vec<_> = fs::read_dir(&backups_dir)
+        .expect("read backups dir")
+        .filter_map(|entry| entry.ok())
+        .collect();
+    assert!(
+        entries.len() <= 10,
+        "expected backups to be trimmed to at most 10 files, got {}",
+        entries.len()
+    );
+
+    let latest_path = backups_dir.join(format!("{latest_backup_id}.json"));
+    assert!(
+        latest_path.exists(),
+        "latest backup {} should be preserved",
+        latest_path.display()
+    );
+
+    // 进一步确认保留的条目包含一些历史文件，说明清理逻辑仅裁剪多余部分
+    let manual_kept = entries
+        .iter()
+        .filter_map(|entry| entry.file_name().into_string().ok())
+        .any(|name| name.starts_with("manual_"));
+    assert!(
+        manual_kept,
+        "cleanup should keep part of the older backups to maintain history"
+    );
+}
diff --git a/src-tauri/tests/provider_commands.rs b/src-tauri/tests/provider_commands.rs
new file mode 100644
index 0000000..098304a
--- /dev/null
+++ b/src-tauri/tests/provider_commands.rs
@@ -0,0 +1,159 @@
+use serde_json::json;
+
+use cc_switch_lib::{
+    get_codex_auth_path, get_codex_config_path, read_json_file, switch_provider_test_hook,
+    write_codex_live_atomic, AppState, AppType, MultiAppConfig, Provider,
+};
+
+#[path = "support.rs"]
+mod support;
+use support::{ensure_test_home, reset_test_fs, test_mutex};
+
+#[test]
+fn switch_provider_updates_codex_live_and_state() {
+    let _guard = test_mutex().lock().expect("acquire test mutex");
+    reset_test_fs();
+    let _home = ensure_test_home();
+
+    let legacy_auth = json!({"OPENAI_API_KEY": "legacy-key"});
+    let legacy_config = r#"[mcp_servers.legacy]
+type = "stdio"
+command = "echo"
+"#;
+    write_codex_live_atomic(&legacy_auth, Some(legacy_config))
+        .expect("seed existing codex live config");
+
+    let mut config = MultiAppConfig::default();
+    {
+        let manager = config
+            .get_manager_mut(&AppType::Codex)
+            .expect("codex manager");
+        manager.current = "old-provider".to_string();
+        manager.providers.insert(
+            "old-provider".to_string(),
+            Provider::with_id(
+                "old-provider".to_string(),
+                "Legacy".to_string(),
+                json!({
+                    "auth": {"OPENAI_API_KEY": "stale"},
+                    "config": "stale-config"
+                }),
+                None,
+            ),
+        );
+        manager.providers.insert(
+            "new-provider".to_string(),
+            Provider::with_id(
+                "new-provider".to_string(),
+                "Latest".to_string(),
+                json!({
+                    "auth": {"OPENAI_API_KEY": "fresh-key"},
+                    "config": r#"[mcp_servers.latest]
+type = "stdio"
+command = "say"
+"#
+                }),
+                None,
+            ),
+        );
+    }
+
+    config.mcp.codex.servers.insert(
+        "echo-server".into(),
+        json!({
+            "id": "echo-server",
+            "enabled": true,
+            "server": {
+                "type": "stdio",
+                "command": "echo"
+            }
+        }),
+    );
+
+    let app_state = AppState {
+        config: std::sync::Mutex::new(config),
+    };
+
+    switch_provider_test_hook(&app_state, AppType::Codex, "new-provider")
+        .expect("switch provider should succeed");
+
+    let auth_value: serde_json::Value =
+        read_json_file(&get_codex_auth_path()).expect("read auth.json");
+    assert_eq!(
+        auth_value
+            .get("OPENAI_API_KEY")
+            .and_then(|v| v.as_str())
+            .unwrap_or(""),
+        "fresh-key",
+        "live auth.json should reflect new provider"
+    );
+
+    let config_text =
+        std::fs::read_to_string(get_codex_config_path()).expect("read config.toml");
+    assert!(
+        config_text.contains("mcp_servers.echo-server"),
+        "config.toml should contain synced MCP servers"
+    );
+
+    let locked = app_state
+        .config
+        .lock()
+        .expect("lock config after switch");
+    let manager = locked
+        .get_manager(&AppType::Codex)
+        .expect("codex manager after switch");
+    assert_eq!(manager.current, "new-provider", "current provider updated");
+
+    let new_provider = manager
+        .providers
+        .get("new-provider")
+        .expect("new provider exists");
+    let new_config_text = new_provider
+        .settings_config
+        .get("config")
+        .and_then(|v| v.as_str())
+        .unwrap_or_default();
+    assert_eq!(
+        new_config_text, config_text,
+        "provider config snapshot should match live file"
+    );
+
+    let legacy = manager
+        .providers
+        .get("old-provider")
+        .expect("legacy provider still exists");
+    let legacy_auth_value = legacy
+        .settings_config
+        .get("auth")
+        .and_then(|v| v.get("OPENAI_API_KEY"))
+        .and_then(|v| v.as_str())
+        .unwrap_or("");
+    assert_eq!(
+        legacy_auth_value, "legacy-key",
+        "previous provider should be backfilled with live auth"
+    );
+}
+
+#[test]
+fn switch_provider_missing_provider_returns_error() {
+    let _guard = test_mutex().lock().expect("acquire test mutex");
+    reset_test_fs();
+
+    let mut config = MultiAppConfig::default();
+    config
+        .get_manager_mut(&AppType::Claude)
+        .expect("claude manager")
+        .current = "does-not-exist".to_string();
+
+    let app_state = AppState {
+        config: std::sync::Mutex::new(config),
+    };
+
+    let err = switch_provider_test_hook(&app_state, AppType::Claude, "missing-provider")
+        .expect_err("switching to a missing provider should fail");
+
+    assert!(
+        err.to_string().contains("供应商不存在"),
+        "error message should mention missing provider"
+    );
+}
diff --git a/src-tauri/tests/support.rs b/src-tauri/tests/support.rs
new file mode 100644
index 0000000..21d947f
--- /dev/null
+++ b/src-tauri/tests/support.rs
@@ -0,0 +1,47 @@
+use std::path::{Path, PathBuf};
+use std::sync::{Mutex, OnceLock};
+
+use cc_switch_lib::{update_settings, AppSettings};
+
+/// 为测试设置隔离的 HOME 目录，避免污染真实用户数据。
+pub fn ensure_test_home() -> &'static Path {
+    static HOME: OnceLock<PathBuf> = OnceLock::new();
+    HOME.get_or_init(|| {
+        let base = std::env::temp_dir().join("cc-switch-test-home");
+        if base.exists() {
+            let _ = std::fs::remove_dir_all(&base);
+        }
+        std::fs::create_dir_all(&base).expect("create test home");
+        std::env::set_var("HOME", &base);
+        #[cfg(windows)]
+        std::env::set_var("USERPROFILE", &base);
+        base
+    })
+    .as_path()
+}
+
+/// 清理测试目录中生成的配置文件与缓存。
+pub fn reset_test_fs() {
+    let home = ensure_test_home();
+    for sub in [".claude", ".codex", ".cc-switch"] {
+        let path = home.join(sub);
+        if path.exists() {
+            if let Err(err) = std::fs::remove_dir_all(&path) {
+                eprintln!("failed to clean {}: {}", path.display(), err);
+            }
+        }
+    }
+    let claude_json = home.join(".claude.json");
+    if claude_json.exists() {
+        let _ = std::fs::remove_file(&claude_json);
+    }
+
+    // 重置内存中的设置缓存，确保测试环境不受上一次调用影响
+    let _ = update_settings(AppSettings::default());
+}
+
+/// 全局互斥锁，避免多测试并发写入相同的 HOME 目录。
+pub fn test_mutex() -> &'static Mutex<()> {
+    static MUTEX: OnceLock<Mutex<()>> = OnceLock::new();
+    MUTEX.get_or_init(|| Mutex::new(()))
+}